Among the various flat panel displays, the TFT LCD is dominating the flat panel display market due to lower power consumption, relatively low manufacturing cost, and no radiation. The TFT LCD device is formed by assembling an array substrate and a color filter substrate with a liquid crystal layer interposed therebetween.
FIG. 1A is a top plan view of one pixel of a conventional amorphous silicon TFT LCD array substrate, and FIG. 1B is a cross-sectional view taken along the line A-A in FIG. 1A. This array substrate comprises: a plurality of gate lines 1 and a plurality of data lines 5 perpendicular to the gate lines 1. The adjacent gate lines and data lines define a pixel area. Each pixel area comprises a TFT as a switching device, a transparent pixel electrode 10, and a part of the common electrode 11. The TFT employs a bottom gate structure by a back channel etched as shown. The TFT comprises a gate electrode 2, a gate insulating layer 4, an active layer 3, a source electrode 6, and a drain electrode 7, as shown in FIG. 1B. A passivation layer 8 covers the above-mentioned components, and a passivation layer via hole 9 is formed in the passivation layer 8 over the drain electrode 7. The transparent electrode 10 is connected with the drain electrode 7 of the TFT via the passivation layer via hole 9. The source electrode 6 is connected with one of the data lines 5. The part of the common electrode 11 forms a storage capacitor with the pixel electrode 10 by overlapping with the pixel electrode 10 (the projection portion in the pixel area). In order to further lower the light leakage within the pixel area, light blocking bars 12 are formed on both sides of the pixel electrode 10 parallel to the data lines 5 in the pixel area. The TFT device can reduce the light-induced leak current in the channel. The light blocking bars 12 are made of the same material as the gate electrode 12 in the same process.
The 5-Mask (photolithography) process as shown in FIG. 2 is a typical manufacturing technology for TFT LCD array substrate at present and mainly comprises the following five steps:
1). forming a gate electrode and gate line, and optionally forming light blocking bars and/or common electrodes simultaneously;
2). forming a gate insulating layer and an active layer;
3). forming a source electrode, a drain electrode, and a data line;
4). forming a passivation layer; and
5). forming a pixel electrode.
Each of the steps comprises three main processes, namely, thin film deposition, forming of the etching mask pattern (coating a photoresist layer, exposing with a mask plate, and developing), and etching. Each of the five steps uses a mask plate to pattern the respective deposited layer. The above process is typical for 5-Mask technology. Other 5-Mask technologies could also be employed by changing the mask plate design and the process flow.
In the TFT LCD array substrate shown in FIGS. 1A and 1B, since the drain electrode is always located in the pixel area, a part of the aperture ratio is always sacrificed, causing a decrease in the aperture ratio. A common method of improving the aperture ratio is to reduce the area occupied by the other components.